The invention relates in general to gas detecting devices and methods and in particular to a new and useful method for determining the presence of diborane in the air.
The invention relates particularly to a method for the highly sensitive detection of diborane in air (ppb range) and operating with high selectivity and speed. It is thus suitable for monitoring work places and rooms, e.g. in micro-electronics in gaseous phase metering processes, or respectively the emission of plants as well as checking the tightness of installations and the like.
Various methods are used for the detection of diborane. Thus there are devices based on the principle of colorimetry. These devices have a detection range of from 0 to 87 ppb, being therefore sensitive and also selective, but they have a long time of enrichment of the compound to be detected (about one hour). Hence they are not suitable for cases of damage. Besides the strips have a limited shelf life; the cost of handling and maintenance is high.
A much faster method is based on dispersive infrared spectrometry (e.g. the MIRAN equipment line of the firm Foxboro Analytical, USA.) One measurement takes only about 10 seconds but the detection limit is as low as 100 ppb, so that many fields of use are left out.
Also chemoluminescence is used for the detection of diborane (e.g. FR No. 2,506,459). The radiation occurring in the reaction of diborane with ozone is measured with a secondary electron multiplier. This method, too, is fast, but the sensitivity is low. The detection limit is 2 ppm.
Lastly it is possible also to employ aerosol ionization gas analysis for the detection of diborane. A radioactive source produces in an ionization chamber an ionization current, which changes in the presence of aerosols, this change of the ionization current being proportional to the aerosol concentration. In the case of diborane, the reaction with an amine is utilized, which leads to well detectable aerosols. While the method is sufficiently fast, the sensitivity is not sufficient. The detection limit is 150 ppb. Besides, the sulfur dioxide content of the air causes a disturbance.